Wisconsin reports pertussis surge as US outbreaks continue

May 23, 2012 (CIDRAP News) – Wisconsin is the latest US state to report a surge in pertussis cases, as outbreaks in a number of states continue to keep health officials busy offering vaccination advice.

The state is experiencing a widespread outbreak, with 1,514 confirmed and probable cases so far, the Wisconsin Department of Health Services said in a news release yesterday. Officials urged residents to get vaccinated, especially with summer camps for children starting in the next few weeks.

The case count suggests that Wisconsin will easily exceed last year's pertussis total. The total of confirmed cases in 2011 was 1,078, the LaCrosse Tribune reported on May 18.

Neighboring Minnesota has its own pertussis outbreak, with cases approaching 700, which is more than last year's total, according to a May 17 report from Minnesota Public Radio. The story said low booster vaccination rates among adults may be part of the problem.

To the west, Montana has had more than 200 cases so far this year, which is the most since a 600-case outbreak in 2005, the state's Department of Public Health and Human Services said in a May 18 press release. It said 18 counties and tribal health jurisdictions have reported cases since January.

New Mexico is also battling the disease, with 112 cases reported for the year as of May 5, according to a May 16 Associated Press (AP) report. It said the number of children with vaccine exemptions in the state has reached 3,400, three times as many as in 1999.

A pertussis roundup provided yesterday by ProMED mail, the online reporting system of the International Society for Infectious Diseases, noted that Maine has had 67 cases so far this year, compared with 50 at this time last year.

A ProMED moderator commented that the current rash of outbreaks probably has multiple causes, including vaccine exemptions, "general under-vaccination," and waning vaccine-induced immunity. The moderator cited studies by Dutch and Australian researchers that revealed antigenic changes in circulating strains of Bordetella pertussis, which may be contributing to a worldwide increase in cases.

David Selvage, MHS, a New Mexico Department of Health epidemiologist, said the vaccine is "the best protection we have against pertussis, but it's probably somewhere in the neighborhood of 80 to 85 percent effective," according to the AP report.